添加回溯算法题目

recall/51.cpp

@@ -0,0 +1,54 @@
+/*
+ * @Description:
+ * @Version: 1.0
+ * @Autor: zhuyijun
+ * @Date: 2021-11-11 22:23:35
+ * @LastEditTime: 2021-11-11 23:02:49
+ */
+#include <bits/stdc++.h>
+using namespace std;
+vector<vector<string>> res;
+bool isVaild(vector<string> &board, int row, int col) {
+  int n = board.size();
+  // 检查列
+  for (int i = 0; i < row; i++) {  // 这是一个剪枝
+    if (board[i][col] == 'Q') {
+      return false;
+    }
+  }
+  // 检查 45度角是否有皇后
+  for (int i = row - 1, j = col - 1; i >= 0 && j >= 0; i--, j--) {
+    if (board[i][j] == 'Q') {
+      return false;
+    }
+  }
+  // 检查 135度角是否有皇后
+  for (int i = row - 1, j = col + 1; i >= 0 && j < n; i--, j++) {
+    if (board[i][j] == 'Q') {
+      return false;
+    }
+  }
+  return true;
+}
+
+void backtrack(vector<string> &board, int row) {
+  if (row == board.size()) {
+    res.push_back(board);
+    return;
+  }
+  auto result = board[row];
+  for (int col = 0; col < result.size(); col++) {
+    if (!isVaild(board, row, col)) {
+      continue;
+    }
+    board[row][col] = 'Q';
+    backtrack(board, row + 1);
+    board[row][col] = '.';
+  }
+}
+vector<vector<string>> solveNQueens(int n) {
+  vector<string> board(n, string(n, '.'));
+  backtrack(board, 0);
+  return res;
+}
+int main() { return 0; }